Air bag coating composition

ABSTRACT

A silicone rubber coating composition which cures into a silicone rubber having a tear strength of 25-50 kN/m and a peeling bond strength of 30-60 N/cm is suited for coating of hollow weave type air bags. A hollow weave type air bag coated with the coating composition can be instantaneously inflated while the bag prevents the silicone rubber film from being peeled from the base fabric, eliminates inflating gas leakage, and retains an acceptable inflation time.

This application is a Divisional of application Ser. No. 10/430,305filed on May 7, 2003, now U.S. Pat. No. 7,059,627 and for which priorityis claimed under 35 U.S.C. § 120; and this application claims priorityof Application No. 2002-134968 filed in Japan on May 10, 2002 under 35U.S.C. § 119; the entire contents of all are hereby incorporated byreference.

This invention relates to a silicone rubber coating composition for anair bag having a hollow weave bag portion, and an air bag coatedtherewith.

BACKGROUND ART

Prior art air bags are made by mating a pair of plain weave fabricpieces coated or lined with rubber on the inner surface, joining themalong the periphery with an adhesive, and stitching the adhesive-joinedportions together, the air bags being referred to as plain weave type.However, when it is desired to accommodate air bags in narrow pockets asavailable in front pillar, roof side rail, center pillar, and quarterpillar zones, the prior art plain weave type air bags lack compactnessdue to the thickness of the stitched portion.

To combat this situation, JP-A 2-158442 proposes an air bag having a bagportion formed by hollow weaving, eliminating a need for adhesive bonds.This air bag is referred to as hollow weave type. The hollow weave typeair bag is fully compact, but raises another problem. Because of thestructure of the hollow weave type air bag, the rubber coating layer isapplied to the outside surface of the air bag as opposed to the plainweave type. Then, upon inflation, the inflating gas acts on the bag fromthe base fabric side as opposed to the plain weave type where the gasacts from the rubber coating side. Although it is desired to ensure thatthe bag be kept inflated for a certain time, the conventional rubbercoating composition used in the plain weave type fails to hold the sameinflation time for the hollow weave type air bag.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a siliconerubber coating composition for air bags of the hollow weave type,capable of holding an acceptable inflation time, and a hollow weave typeair bag having a coating layer thereof.

Analyzing the factors associated with inflating gas leakage, theinventor has found that when a hollow weave type air bag is coated witha silicone rubber coating composition, especially of the additionreaction cure type, which cures into a silicone rubber having a tearstrength of at least 25 kN/m and a peeling bond strength of at least 30N/cm, the resulting air bag is capable of retaining an acceptableinflation time.

Accordingly, the present invention provides a silicone rubber coatingcomposition for an air bag having a hollow weave bag portion, the curedcomposition having a tear strength of at least 25 kN/m and a peelingbond strength of at least 30 N/cm.

The present invention also provides an air bag having a hollow weave bagportion, having a rubber coating layer of the coating compositionthereon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The silicone rubber coating composition of the invention suitable foruse in hollow weave type air bags is preferably of the addition reactioncuring type, typically comprising

(A) 100 parts by weight of an organopolysiloxane containing on theaverage at least two alkenyl groups in a molecule,

(B) an amount of an organohydrogenpolysiloxane containing at least twosilicon atom-bonded hydrogen atoms in a molecule to give 1 to 7 moles ofsilicon atom-bonded hydrogen atoms per mole of silicon atom-bondedalkenyl groups in component (A),

(C) a catalytic amount of an addition reaction catalyst,

(D) 1 to 50 parts by weight of finely divided silica having a specificsurface area of at least 50 m²/g as measured by the BET method, and

(E) 0.1 to 10 parts by weight of an organosilicon compound having atackifying functional group.

The organopolysiloxane (A) serving as a base component of thecomposition contains on the average at least two alkenyl groups eachattached to a silicon atom in a molecule. The alkenyl groups are usuallythose of about 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms,including vinyl, allyl, butenyl, pentenyl, hexenyl, and heptenyl, withvinyl being most preferred.

In the organopolysiloxane, silicon atom-bonded alkenyl groups may belocated, for example, at ends and/or side chains of the molecular chain.The organopolysiloxane contains silicon atom-bonded organic groups otherthan the alkenyl groups. Such other organic groups include unsubstitutedor halo-substituted monovalent hydrocarbon groups of about 1 to 12carbon atoms, preferably about 1 to 10 carbon atoms, for example, alkylgroups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl,and heptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl;aralkyl groups such as benzyl and phenethyl; and halogenated alkylgroups such as chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl,with methyl and phenyl being preferred. The content of alkenyl groups incomponent (A) is preferably about 0.001 to about 10 mol %, especiallyabout 0.01 to about 5 mol % of the entire monovalent organic groups (orsubstituted or unsubstituted monovalent hydrocarbon groups) bonded tosilicon atoms.

The molecular structure of the organopolysiloxane (A) may be a straight,partially branched straight, cyclic or branched chain, for example.Preferred is a straight chain diorganopolysiloxane whose backboneconsists essentially of recurring diorganosiloxane units and whosemolecular chain is blocked with a triorganosiloxy group at either end.It is noted that the organo groups used herein can include alkenyl. Theorganopolysiloxane (A) should preferably have a viscosity of 100 to500,000 mPa·s at 25° C., more preferably 300 to 100,000 mPa·s at 25° C.because the resulting silicone rubber has excellent physical propertiesand the resulting composition becomes easy to handle.

Examples of the organopolysiloxane (A) include trimethylsiloxyend-capped dimethylsiloxane-methylvinylsiloxane copolymers,trimethylsiloxy end-capped methylvinylpolysiloxane, trimethylsiloxyend-capped dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxanecopolymers, dimethylvinylsiloxy end-capped dimethylpolysiloxane,dimethylvinylsiloxy end-capped methylvinylpolysiloxane,dimethylvinylsiloxy end-capped dimethylsiloxane-methylvinylsiloxanecopolymers, dimethylvinylsiloxy end-cappeddimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers,trivinylsiloxy end-capped dimethylpolysiloxane, organopolysiloxanecopolymers consisting of siloxane units represented by the formula: R¹₃SiO_(1/2), siloxane units represented by the formula: R¹ ₂R²SiO_(1/2),units represented by the formula: R¹ ₂SiO and a minor amount of siloxaneunits represented by the formula: SiO₂, organopolysiloxane copolymersconsisting of siloxane units represented by the formula: R¹ ₃SiO_(1/2),siloxane units represented by the formula: R¹ ₂R²SiO_(1/2), and siloxaneunits represented by the formula: SiO₂, organopolysiloxane copolymersconsisting of siloxane units represented by the formula: R¹₂R²SiO_(1/2), units represented by the formula: R¹ ₂SiO and siloxaneunits represented by the formula: SiO₂, organopolysiloxane copolymersconsisting of siloxane units represented by the formula: R¹R²SiO and aminor amount of siloxane units represented by the formula: R¹ ₂SiO_(3/2)or R²SiO_(3/2), and mixtures of two or more of the foregoing.

Throughout the specification, the term “end-capped” used in connectionwith siloxanes means that a siloxane is capped with a specified group ateach end of its molecular chain.

In the above formulae, R¹ is a substituted or unsubstituted monovalenthydrocarbon group other than alkenyl groups, for example, alkyl groupssuch as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, andheptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl; aralkylgroups such as benzyl and phenethyl; and halogenated alkyl groups suchas chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl. R² is analkenyl group such as vinyl, allyl, butenyl, pentenyl, hexenyl orheptenyl.

From the requirement that the cured silicone rubber have a tear strengthof at least 25 kN/m and a peeling bond strength of at least 30 N/cm, thealkenyl-bearing organopolysiloxane (A) is preferably a combination of analkenyldiorganosiloxy end-capped (alkenyl group-free backbone)diorganopolysiloxane (e.g., dimethylvinylsiloxy end-cappeddimethylpolysiloxane) with an alkenyldiorganosiloxy or triorganosiloxyend-capped diorganosiloxane-alkenylorganosiloxane copolymer (e.g.,dimethylvinylsiloxy or trimethylsiloxy end-cappeddimethylsiloxane-vinylmethylsiloxane copolymer). It is noted that theorgano groups used herein should exclude alkenyl.

The organohydrogenpolysiloxane (B) reacts with component (A) and servesas a crosslinking agent. Its molecular structure is not critical. Any ofstraight, cyclic, branched and three-dimensional network structure(resinous) manufactured in the prior art may be used. It should containat least two, preferably at least three silicon atom-bonded hydrogenatoms (hydrosilyl groups represented by SiH) in a molecule. Typically,the organohydrogenpolysiloxane contains 2 to about 500, preferably 3 toabout 200, more preferably 3 to about 100 SiH groups. Theorganohydrogenpolysiloxane used herein often has the averagecompositional formula (1).R³ _(b)H_(c)SiO_((4-b-c)/2)  (1)

In formula (1), R³ is an aliphatic unsaturation-free, substituted orunsubstituted monovalent hydrocarbon group, preferably having 1 to 10carbon atoms, attached to a silicon atom. Suitable monovalenthydrocarbon groups represented by R³ include alkyl groups such asmethyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl,neopentyl, hexyl, cyclohexyl, octyl, nonyl and decyl, aryl groups suchas phenyl, tolyl, xylyl and naphthyl, aralkyl groups such as benzyl,phenylethyl and phenylpropyl, and substituted ones of the foregoing inwhich some or all of the hydrogen atoms are substituted with halogenatoms (e.g., fluoro, bromo or chloro), such as chloromethyl,chloropropyl, bromoethyl and trifluoropropyl. The preferred monovalenthydrocarbon groups represented by R³ are alkyl and aryl groups, withmethyl and phenyl being most preferred. The subscript b is a positivenumber of 0.7 to 2.1, c is a positive number of 0.001 to 1.0, and thesum of b+c is 0.8 to 3.0, and preferably, b is 1.0 to 2.0, c is 0.01 to1.0, and b+c is 1.5 to 2.5.

At least two, preferably at least three SiH groups are included permolecule while they may be located either at ends or midway of themolecular chain or both. The molecular structure of theorganohydrogenpolysiloxane may be straight, cyclic, branched orthree-dimensional network structure. For the physical properties of theresulting silicone rubber and ease of handling of the resultingcomposition, the number of silicon atoms per molecule (that is, degreeof polymerization) is preferably from 2 to about 1,000, more preferably3 to about 300, even more preferably 4 to about 150. For the samereason, the preferred organohydrogen-polysiloxane is liquid at roomtemperature (25° C.) and specifically, has a viscosity at 25° C. ofabout 0.1 to 5,000 mPa·s, preferably about 0.5 to 1,000 mPa·s, morepreferably about 5 to 500 mPa·s.

Examples of the organohydrogenpolysiloxane (B) include trimethylsiloxyend-capped methylhydrogenpolysiloxane, trimethylsiloxy end-cappeddimethylsiloxane-methylhydrogensiloxane copolymers, trimethylsiloxyend-capped dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxanecopolymers, dimethylhydrogensiloxy end-capped dimethylpolysiloxane,dimethylhydrogensiloxy end-cappeddimethylpolysiloxane-methylhydrogensiloxane copolymers,dimethylhydrogensiloxy end-capped dimethylsiloxane-methylphenylsiloxanecopolymers, dimethylhydrogensiloxy end-cappeddimethylphenylpolysiloxane, organopolysiloxane copolymers consisting ofsiloxane units represented by the formula: R¹ ₃SiO_(1/2), siloxane unitsrepresented by the formula: R¹ ₂HSiO_(1/2) and a minor amount ofsiloxane units represented by the formula: SiO₂, organopolysiloxanecopolymers consisting of siloxane units represented by the formula: R¹₂HSiO_(1/2) and a minor amount of siloxane units represented by theformula: SiO₂, organopolysiloxane copolymers consisting of siloxaneunits represented by the formula: R¹HSiO and a minor amount of siloxaneunits represented by the formula: R¹SiO_(3/2) or HSiO_(3/2), andmixtures of two or more of the foregoing. It is noted that R¹ is asubstituted or unsubstituted monovalent hydrocarbon group other thanalkenyl, which is as described and exemplified above.

From the requirement that the cured silicone rubber have a tear strengthof at least 25 kN/m and a peeling bond strength of at least 30 N/cm, theorganohydrogenpolysiloxane (B) is preferably a combination of atriorganosiloxy end-capped organohydrogenpolysiloxane (e.g.,trimethylsiloxy end-capped methylhydrogenpolysiloxane) with atriorganosiloxy or diorganohydrogensiloxy end-cappeddiorganosiloxane-organohydrogensiloxane copolymer (e.g., trimethylsiloxyor dimethylhydrogensiloxy end-cappeddimethylsiloxane-methylhydrogensiloxane copolymer). It is noted that theorgano groups used herein should exclude alkenyl.

Component (B) is compounded in such amounts that 1 to 7 moles,preferably 2 to 5 moles of silicon atom-bonded hydrogen atoms incomponent (B) are available per mole of silicon atom-bonded alkenylgroups in component (A). If less than 1 mole of silicon atom-bondedhydrogen atoms in component (B) are available per mole of siliconatom-bonded alkenyl groups in component (A), then the coating film hasinsufficient strength. If more than 7 moles of silicon atom-bondedhydrogen atoms in component (B) are available per mole of siliconatom-bonded alkenyl groups in component (A), then the coating filmsuffers an extreme loss of heat resistance.

Component (C) is any catalyst which can promote the addition reactionbetween alkenyl groups in component (A) and SiH groups in component (B).Suitable catalysts include platinum group metals and compounds thereof,for example, platinum, palladium, rhodium, etc., chloroplatinic acid,alcohol-modified chloroplatinic acid, coordinate compounds ofchloroplatinic acid with olefins, vinylsiloxanes or acetylene compounds,tetrakis(triphenylphosphine)palladium andchlorotris(triphenylphosphine)rhodium. Of these, platinum compounds arepreferred. Component (C) is used in catalytic amounts, preferably suchas to give 1 to 500 ppm, more preferably 10 to 100 ppm of catalyticmetal element based on the weight of components (A) and (B) combined.With less than 1 ppm of component (C), the addition reaction may besubstantially retarded or the composition may not cure. More than 500ppm of component (C) may adversely affect the heat resistance of thecured polysiloxane composition.

Component (D) is finely divided silica serving as a reinforcing agent.It imparts high tear strength to the inventive composition. Using finelydivided silica as a reinforcing agent, it becomes possible to form acoating film meeting the tear properties required by the invention. Thefinely divided silica should have a specific surface area of at least 50m²/g, preferably 50 to 400 m²/g, more preferably 100 to 300 m²/g, asmeasured by the BET method. A silica powder with a specific surface areaof less than 50 m²/g fails to impart satisfactory tear strength.

As long as the specific surface area is within the above-specifiedrange, component (D) may be any of silica powders which are ordinarilyused as a reinforcing filler for silicone rubber, for example, fumedsilica and precipitated silica. Such silicas may be used alone or inadmixture. The finely divided silica may be used as such although it ispreferred to use silicas treated with organosilicon compounds such asmethylchlorosilanes (e.g., trimethylchlorosilane, dimethyldichlorosilaneand methyltrichlorosilane), dimethylpolysiloxane, hexaorganodisilazanes(e.g., hexamethyldisilazane, divinyltetramethyldisilazane anddimethyltetravinyldisilazane) in order to impart good flow to theinventive composition.

Component (D) is compounded in amounts of 1 to 50 parts by weight,preferably 5 to 15 parts by weight per 100 parts by weight of component(A). Too small amounts of component (D) fail to achieve the requiredtear strength whereas too large amounts of component (D) adverselyaffect the flow of the composition to impede coating operation.

Component (E) is intended to improve the adhesion of the composition tosynthetic fiber woven fabric bases or non-woven fabric bases for airbags, or thermoplastic resin sheets or film bases. From the standpointof imparting self-tack to addition reaction type silicone rubbercompositions, a silicon compound having a tackifying functional group isselected as component (E). Examples of the functional group include analkenyl group bonded to a silicon atom, such as vinyl or allyl; an epoxygroup bonded to a silicon atom through a carbon atom or atoms, such asγ-glycidoxypropyl or β-(3,4-epoxycyclohexyl)ethyl; a (meth)acryloxygroup such as γ-acryloxypropyl or γ-methacryloxypropyl; an alkoxysilylgroup such as an alkoxysilyl group (e.g., trimethoxysilyl,triethoxysilyl or methyldimethoxysilyl) bonded to a silicon atom throughan alkylene group which may contain one or two ester, urethane or etherstructures; an organosilane having a SiH group, a straight or cyclicsiloxane oligomer having 3 to 50 silicon atoms, especially 5 to 20silicon atoms, and an (alkoxy)silyl-modified triallyl isocyanurate andsiloxane derivatives thereof. A silicon compound having such functionalgroups of two or more types per molecule is preferred. Examples of thesilicon compound having such functional groups are given below.

Component (E) is compounded in amounts of 0.1 to 10 parts by weight,preferably 0.5 to 5 parts by weight, per 100 parts by weight ofcomponent (A). Too small amounts of component (E) may fail to provide asatisfactory peeling bond strength whereas too large amounts ofcomponent (E) may be uneconomical.

In addition to the above-described components (A) to (E), the coatingcomposition may further include optional components. Typically, there iscompounded any of regulators well known as exerting a cure-restrainingeffect to the addition reaction catalyst. Suitable regulators includephosphorus-containing compounds such as triphenylphosphine,nitrogen-containing compounds such as tributylamine,tetramethylethylenediamine and benzotriazole, sulfur-containingcompounds, acetylene compounds, compounds containing two or more alkenylgroups, hydroperoxy compounds, and maleic acid derivatives. The extentof the cure-restraining effect by the regulator largely varies with thechemical structure of the regulator. Therefore, the amount of theregulator added should be determined to be optimum for the particularregulator used. As a general rule, too small amounts of the regulatorfail to provide long-term shelf stability at room temperature whereastoo large amounts rather interfere with curing.

Other optional components include, for example, inorganic fillers suchas crystalline silica, hollow fillers, silsesquioxane, fumed titaniumdioxide, magnesium oxide, zinc oxide, iron oxide, aluminum hydroxide,magnesium carbonate, calcium carbonate, zinc carbonate, layer mica,carbon black, diatomaceous earth, and glass fibers, as well as theforegoing fillers which have been surface treated with organosiliconcompounds such as organoalkoxysilanes, organochlorosilanes,organosilazanes, and low molecular weight siloxanes. Besides, siliconerubber powder and silicone resin powder are also useful.

Other optional components which can be used in the coating compositionas long as they do not compromise the objects of the invention includeorganopolysiloxanes containing one silicon atom-bonded hydrogen atom oralkenyl group per molecule, organopolysiloxanes free of a siliconatom-bonded hydrogen atom or alkenyl group, organic solvents,anti-crepe-hardening agents, plasticizers, thixotropic agents, pigments,dyes, and mildew-proof agents.

The coating composition can be prepared by mixing the essential andoptional components. The composition thus obtained is used as a coatingagent for hollow weave type air bags. To this end, the coatingcomposition is preferably liquid and especially, has a viscosity ofabout 50 to about 200 Pa·s at 25° C.

The coating composition of the invention can be cured under conditionswhich are well known to conventional addition reaction curing siliconerubber compositions, typically at a temperature of about 120 to 180° C.for a time of about 1 to 10 minutes.

The coating composition of the invention cures into a product orsilicone rubber which should have a tear strength of at least 25 kN/m,usually 25 to 50 kN/m, preferably 27 to 50 kN/m, more preferably 30 to40 kN/m, and a peeling bond strength of at least 30 N/cm, usually 30 to60 N/cm, preferably 35 to 50 N/cm, more preferably 40 to 50 N/cm. Withtoo low a tear strength, the coating layer at the joint can be crackedupon inflation of the air bag, failing to retain an inflation time. Withtoo low a peeling bond strength, the coating layer at the joint can beseparated from the base fabric upon inflation of the air bag, failing toretain an inflation time.

It is noted that the tear strength is measured according to JIS K6249.The peeling bond strength is measured by sandwiching the compositionbetween a pair of air bag-forming nylon 66 (420 denier) woven fabricpieces so that the composition has a thickness of 0.5 mm, curing thecomposition at 170° C. and a pressure of 5 kgf/cm² for 1 minute, cuttinginto a specimen of 2.5 cm wide and 20 cm long and performing a peelingbond strength test on the specimen at a peeling angle of 180° and apulling speed of 50 mm/min.

In the practice of the invention, the hollow weave type air bag on whicha silicone rubber layer is to be formed by coating and curing theabove-described composition may be of well-known construction, forexample, hollow weave type air bags using as the base fabric wovenfabrics of synthetic fibers such as nylon 66, nylon 6, polyester,aramid, polyamide, and polyester fibers.

Any conventional technique may be employed in coating the composition tosuch hollow weave type air bags. The buildup of the coating layer orsurface coverage is preferably about 15 to 150 g/m², more preferablyabout 15 to 80 g/m², most preferably about 20 to 40 g/m².

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. All parts are by weight and the viscosity is ameasurement at 25° C. The tackifiers X, Y and Z used are identifiedbelow.

Example 1

A composition A was prepared by mixing the following: 80 parts of adimethylvinylsiloxy end-capped dimethylpolysiloxane and having aviscosity of 10 Pa·s, 4 parts of a trimethylsiloxy end-cappeddimethylsiloxane-methylvinylsiloxane copolymer containing 5 mol % ofvinylmethylsiloxane units and 95 mol % of dimethylsiloxane units in thediorganosiloxane units of the backbone and having a viscosity of 0.7Pa·s, 17 parts of hydrophobic silica treated with trimethylsilyl groupsand having a specific surface area of 120 m²/g, 1.0 part of atrimethylsiloxy end-capped methylhydrogenpolysiloxane (siliconatom-bonded hydrogen atom content=1.45 wt %) having a viscosity of 5mPa·s, 2.2 parts of a dimethylsiloxane-methylhydrogensiloxane copolymerhaving silicon atom-bonded hydrogen atoms at both ends and side chainsof the molecular chain (silicon atom-bonded hydrogen atom content=0.54wt %) and having a viscosity of 12 mPa·s (giving H/Vi=3.9 mol/mol), 0.05part of 1-ethynyl cyclohexanol, an amount of a complex of chloroplatinicacid with divinyltetramethyldisiloxane to give 30 ppm of platinum metalbased on the total weight of the components, 1.5 parts of Tackifier X,0.5 part of Tackifier Y, and 0.5 part of octyl titanate.

Note that “H/Vi” is a molar ratio of a total SiH group content incomponent (B) to a total vinyl group content in vinyl-containingorganopolysiloxanes as component (A).

The composition was cured at 150° C. for 5 minutes. A sheet was formedtherefrom and measured for physical properties according to JIS K6249. Apeeling bond strength test was carried out by sandwiching thecomposition between a pair of air bag-forming nylon 66 (420 denier)woven fabric pieces so that the composition had a thickness of 0.5 mm,curing the composition at 170° C. and a pressure of 5 kgf/cm² for 1minute, and cutting into a specimen of 2.5 cm×20 cm.

Using a coater, the silicone rubber composition was uniformly coated toa hollow weave air bag, without any variation in buildup, to apermissible minimum coverage. The coating was cured by heating at 170°C. for one minute in an oven, completing a hollow weave air bag. Aninflation test was performed on the air bag by instantaneously injectingair into the bag at a pressure of 7 kg/cm² within 3 seconds and visuallyinspecting air-tightness, that is, observing whether the silicone rubberfilm was peeled off. The results are shown in Table 1.

Example 2

A composition B was prepared by mixing the following: 17 parts of adimethylvinylsiloxy end-capped dimethylpolysiloxane and having aviscosity of 100 Pa·s, 33 parts of a dimethylvinylsiloxy end-cappeddimethylpolysiloxane and having a viscosity of 10 Pa·s, 30 parts of adimethylvinylsiloxy end-capped dimethylpolysiloxane and having aviscosity of 1 Pa·s, 3 parts of a trimethylsiloxy end-cappeddimethylsiloxane-methylvinylsiloxane copolymer containing 10 mol % ofvinylmethylsiloxane units and 90 mol % of dimethylsiloxane units in thediorganosiloxane units of the backbone and having a viscosity of 0.7Pa·s, 5 parts of an organopolysiloxane resin consisting of 39.5 mol % of(CH₃)₃SiO_(1/2) units, 6.5 mol % of (CH₃)₂(CH₂═CH)SiO_(1/2) units, and54 mol % of SiO₂ units, 22 parts of hydrophobic silica treated withtrimethylsilyl groups and having a specific surface area of 170 m²/g,1.8 part of a trimethylsiloxy end-capped methylhydrogenpolysiloxane(silicon atom-bonded hydrogen atom content=1.14 wt %) having a viscosityof 45 mPa·s, 5.3 parts of a dimethylsiloxane-methylhydrogensiloxanecopolymer having silicon atom-bonded hydrogen atoms at both ends andside chains of the molecular chain (silicon atom-bonded hydrogen atomcontent=0.54 wt %) and having a viscosity of 12 mPa·s (giving H/Vi=3.4mol/mol), 0.03 part of 1-ethynyl cyclohexanol, an amount of a complex ofchloroplatinic acid with divinyltetramethyldisiloxane to give 15 ppm ofplatinum metal based on the total weight of the components, 0.4 part ofTackifier X, 0.2 part of Tackifier Z, and 0.2 part of octyl titanate.

As in Example 1, cured physical properties were measured, and a peelingbond strength test and an inflation test performed. The results areshown in Table 1.

Comparative Example 1

A composition C was prepared by mixing the following: 17 parts of adimethylvinylsiloxy end-capped dimethylpolysiloxane and having aviscosity of 100 Pa·s, 33 parts of a dimethylvinylsiloxy end-cappeddimethylpolysiloxane and having a viscosity of 10 Pa·s, 37 parts of adimethylvinylsiloxy end-capped dimethylpolysiloxane and having aviscosity of 1 Pa·s, 22 parts of hydrophobic silica treated withtrimethylsilyl groups and having a specific surface area of 170 m²/g, 1part of a trimethylsiloxy end-capped methylhydrogenpolysiloxane (siliconatom-bonded hydrogen atom content=1.14 wt %) having a viscosity of 45mPa·s, 3 parts of a dimethylsiloxane-methylhydrogensiloxane copolymerhaving silicon atom-bonded hydrogen atoms at both ends and side chainsof the molecular chain (silicon atom-bonded hydrogen atom content=0.54wt %) and having a viscosity of 12 mPa·s (giving H/Vi=4.1 mol/mol), 0.06part of 1-ethynyl cyclohexanol, an amount of a complex of chloroplatinicacid with divinyltetramethyldisiloxane to give 15 ppm of platinum metalbased on the total weight of the components, 1.5 parts of Tackifier X,and 0.5 part of Tackifier Z. As in Example 1, cured physical propertieswere measured, and a peeling bond strength test and an inflation testperformed. The results are shown in Table 1.

Comparative Example 2

A composition D was prepared by mixing the following: 50 parts of adimethylvinylsiloxy end-capped dimethylpolysiloxane and having aviscosity of 10 Pa·s, 67 parts of a dimethylvinylsiloxy end-cappeddimethylpolysiloxane and having a viscosity of 1 Pa·s, 33 parts ofhydrophobic silica treated with trimethylsilyl groups and having aspecific surface area of 170 m²/g, 13 parts of an organopolysiloxaneresin consisting of 39.5 mol % of (CH₃)₃SiO_(1/2) units, 6.5 mol % of(CH₃)₂(CH₂═CH)SiO_(1/2) units, and 54 mol % of SiO₂ units, 2.7 part of atrimethylsiloxy end-capped methylhydrogenpolysiloxane (siliconatom-bonded hydrogen atom content=1.14 wt %) having a viscosity of 45mPa·s, 8.3 parts of a dimethylsiloxane-methylhydrogensiloxane copolymerhaving silicon atom-bonded hydrogen atoms at both ends and side chainsof the molecular chain (silicon atom-bonded hydrogen atom content=0.54wt %) and having a viscosity of 12 mPa·s (giving H/Vi=3.3 mol/mol), 0.05part of 1-ethynyl cyclohexanol, an amount of a complex of chloroplatinicacid with divinyltetramethyldisiloxane to give 20 ppm of platinum metalbased on the total weight of the components, 1.5 parts of Tackifier X,0.5 part of Tackifier Y, and 0.5 part of octyl titanate. As in Example1, cured physical properties were measured, and a peeling bond strengthtest and an inflation test performed. The results are shown in Table 1.

TABLE 1 Comparative Example Example 1 2 1 2 Hardness (Durometer A) 35 4534 44 Tensile strength (MPa) 3.7 6.8 6.5 6.5 Elongation at shear (%) 360360 420 260 Tear strength (kN/m) 27 31 24 21 Peeling bond strength(N/cm) 35 47 5 25 Inflation test no peel no peel peeled peeled

A hollow weave type air bag coated with the coating composition of theinvention can be instantaneously inflated while the bag prevents thesilicone rubber film from being peeled from the base fabric,substantially eliminates the risk of gas leakage, and retains anacceptable inflation time.

Japanese Patent Application No. 2002-134968 is incorporated herein byreference.

Reasonable modifications and variations are possible from the foregoingdisclosure without departing from either the spirit or scope of thepresent invention as defined by the claims.

1. A silicone rubber coating composition for an air bag having a hollowweave bag portion comprising: (A) 100 parts by weight of anorganopolysiloxane containing on the average at least two alkenyl groupsin a molecule; (B) an amount of an organohydrogenpolysiloxane containingat least two silicon atom-bonded hydrogen atoms in a molecule to give 1to 7 moles of silicon atom-bonded hydrogen atoms per mole of siliconatom-bonded alkenyl groups in component (A); (C) a catalytic amount ofan addition reaction catalyst; (D) 1 to 50 parts by weight of finelydivided silica having a specific surface area of at least 50 m²/g asmeasured by the BET method; and (E) 0.1 to 10 parts by weight of anorganosilicon compound having a tackifying functional group; wherein thealkenyl group-containing organopolysiloxane (A) comprises analkenyldiorganosiloxy end-capped diorganopolysiloxane and analkenyldiorganosiloxy or triorganosiloxy end-cappeddiorganosiloxane-alkenylorganosiloxane copolymer, theorganohydrogenpolysiloxane (B) comprises a triorganosiloxy end-cappedorganohydrogenpolysiloxane and a triorganosiloxy or diorganohydrogensiloxy end-capped diorganosiloxane-organohydrogensiloxane copolymer, incomponent (B), a molar ratio of a total SiH group content in thetriorganosiloxy end-capped organohydrogenpolysiloxane to a total SiHgroup content in the triorganosiloxy or diorganohydrogensiloxyend-capped diorganosiloxane-organohydrogensiloxane copolymer is 0.7 to1.2, and the cured composition has a tear strength of at least 25 kN/mand a peeling bond strength of at least 30 N/cm.
 2. The composition ofclaim 1 wherein the organopolysiloxane (A) is a member selected from thegroup consisting of: trimethylsiloxy end-cappeddimethylsiloxane-methylvinylsiloxane copolymers; trimethylsiloxyend-capped dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxanecopolymers; dimethylvinylsiloxy end-capped dimethylpolysiloxane;dimethylvinylsiloxy end-capped dimethylsiloxane-methylvinylsiloxanecopolymers; and dimethylvinylsiloxy end-cappeddimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers. 3.The composition of claim 1 wherein the organohydrogenpolysiloxane (B)reacts with component (A) and serves as a crosslinking agent.
 4. Thecomposition of claim 1 wherein Component (B) is present in an amountsuch that 2 to 5 moles of silicon atom-bonded hydrogen atoms incomponent (B) are available per mole of silicon atom-bonded alkenylgroups in component (A).
 5. The composition of claim 1 wherein thecatalyst (C) is selected from the group consisting of platinum groupmetals and compounds thereof.
 6. The composition of claim 1 wherein thefinely divided silica (D) has a specific surface area of 100 to 300m²/g, as measured by the BET method.
 7. The composition of claim 1,wherein: the tackifying functional group of the organosilicon compound(E) is selected from the group consisting of a vinyl group, an allylgroup, an epoxy group bonded to a silicon atom through one or morecarbon atoms, a (meth)acryloxy group, and an alkoxysilyl group bonded toa silicon atom through an alkylene group; or the organosilicon compound(E) is selected from the group consisting of an organosilane having aSiH group, a straight or cyclic siloxane oligomer having 3 to 50 siliconatoms, and an (alkoxy)silyl-modified triallyl isocyanurate.
 8. Thecomposition of claim 1, wherein the organohydrogenpolysiloxane (B) is amember selected from the group consisting of: trimethylsiloxy end-cappedmethylhydrogenpolysiloxane; trimethylsiloxy end-cappeddimethylsiloxane-methylhydrogensiloxane copolymers; trimethylsiloxyend-capped dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxanecopolymers; and dimethylhydrogensiloxy end-cappeddimethylpolysiloxane-methylhydrogensiloxane copolymers.